This apparatus and process involves the plating of one end of cut, straightened wires typically used as probe needle blanks for quality assurance testing of computer chips and other integrated circuits. These blanks are typically made of a tungsten or rhenium-tungsten alloy and the plating is typically a nickel electroplating, but other alloys and plating material could be used as well.
In the industry today, one end of these wires is nickel plated for solderability (solder will not stick to unplated tungsten). The other end cannot be plated, since it is electrochemically etched to a point. The current practice involves loading these probe needle blanks into a fixture where individual electrical contact is made and lowering them into a plating solution or bath to the desired depth of plating. The power supply is then turned on, supplying power to the individual probes and to the plating anode, and the plating process commences. The drawback of this process is simply the time and labor involved. Each needle blank must be handled individually in the loading and unloading process. Typically, 30 or 40 pieces are plated at once.
The present invention and process enables plating to be performed in lots of thousands at a time. It can naturally be done much less expensively. The process has several distinguishing characteristics.
A group of parts are dropped into a specially designed fixture (a group being hundreds to thousands of parts depending on the size of the fixture and the diameter of the parts). The fixture consists of a number of unique components (see FIG. 1).
The pressurized gas supply is used to keep the upper cap free of the plating solution. Air pressure is not needed if the rate of plating is fast enough to cause enough hydrogen gas to evolve to collect in the cap.
The hole in the middle plate should be no larger than the hole in the cap and should be positioned closer to the bottom plate. This will allow the parts to move freely when the fixture is put in motion.
Another unique feature of this apparatus is the motion imparted to it. This motion can be imparted by two linear actuators mounted horizontally at right angles to each other, and synchronized. It also can be done rather simply by an offset cam, in a spring-loaded fixture (see FIG. 2).
The purpose of this oscillating type of motion will be to impart some centrifugal force to the parts which will tend to keep them in intimate contact with the cap, thereby assuring that electrical contact will be maintained. It will also assure that parts will lean in one direction and then another direction, thereby making certain that there is relative movement between the parts. This will assure even coverage over the surface in the plating operation and prevent the parts from plating together.
In order to assure even distribution of the plating over the entire surface to be plated, good general plating practices must be followed, including shielding the anodes to "break up" the lines of force, maintaining proper temperature and pH, keeping the plating solution clean, etc.